$x value lost?

[Mhaxx]

Why does parser loose values?

EXAMPLE:

My scanner:
...
{kw_program}    { free(yylval.string); yylval.string = strdup(yytext);
return PROGRAM; }
{kw_return}    { free(yylval.string); yylval.string = strdup(yytext); return
RETURN; }
{kw_end}    { free(yylval.string); yylval.string = strdup(yytext); return
END; }

My parser:
start: PROGRAM RETURN END;    { printf($1); printf($2); printf($3); }

If the input is "program Return end" then the output is "endend"!!! Why?!?

I think $1 and $2 were lost during the process... there's something I can't
understand...

Mhaxx